Different
numbers of species of tenrecs are recognised, from 23 (Nowak 1991) to 34
(MacDonald 1995). There are three subfamilies: the Potamogalinae (otter
shrews), the Oryzoryctinae and the Tenrecinae. The tenrecids are remarkable
in having the greatest diversity of any extant lipotyphlan family, and yet
are confined largely to Madagascar. The otter shrews are also found in West
and central Africa. Tenrecs have retained many ancestral characters of placental
mammals, including a low and variable body temperature, retention of a common
opening for both the urogenital and anal tracts (the cloaca), and undescended
testes in the male. The dental formula of tenrecs varies considerably between
species, reflecting the diversity of the family: i2-3/2-3, c1/1, pm2-3/2-3,
m2-4/2-3 = 32 - 40. The upper molars are zalambdodont, except in the African
otter shrews, in which they are dilambdodont.

Members
of the subfamily Tenrecinae are relatively large and highly variable in
body form. All have spines, which are barbed and detachable in some species,
and controlled by a well-developed muscle called the panniculus carnosus.
Other genera have soft fur. The mammae are often numerous - Tenrec ecaudatus
has 12 pairs. The species of the subfamily Oryzoryctinae are small and lack
spines. Most are shrew-like or mole-like, and one species in the genus Limnogale
is aquatic. The Potamogalinae contains three species, all of which are aquatic
and are termed otter shrews. They are well adapted for aquatic life, and
resemble otters in overall appearance. They perhaps represent an early branch
of the tenrec family.